Comprehensive organic chemistry for IIT JEE main and advanced

There is another rule called as lowest sum rule popularly used for theorganic compounds having functional groups, also can be applied here.. After amino group the groups with only prefix

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Preface Purpose and mission

This book is intended to become a useful companion for the Engineering TestAspirants of India in areas of accuracy, usability, relevance for theexamination, flexibility, and connection with their needs This text wouldevolve over the years and should eliminate much of the cost for owningseveral costly top-quality college-level organic chemistry texts, by puttingtogether the relevant material in one book, and, we hope would contributeeventually to the building of our nation by creating top quality minds

Author

The author of this book, Amitava Mazumder, had finished his graduation inEngineering from N.I.T – Durgapur and his Post Graduation in IndustrialMetallurgy from Jadavpur University-Kolkata, and has more than ten yearsexperience of teaching Chemistry to the Engineering Entrance Test aspirants

in Delhi, Kota and Dubai He presented his thesis for InternationalConference for Manufacturing in Dhaka, Bangladesh in 2000 and publishedhis paper in the proceedings of the same conference

Amitava intends that this book should keep on evolving by contributionsfrom all in the student and teaching community and therefore welcomecomments and suggestions so that he can better serve his dream of creatingwell informed and thoroughly prepared engineering aspirants

About this book

One of the main difficulties students have with organic chemistry isorganizing the information in their minds An engineering entrance aspirantvery quickly will learn over hundreds of chemical reactions Consequently, it

is vital that students take time to not only organize the information, but also

to understand it Indeed, excellent organic chemistry professors will tell,contrary to popular belief, one do not really need to memorize anything fororganic chemistry, instead, one simply needs to understand it By trulylearning something, rather than memorizing it, the students will be able toapply concepts beyond what they are memorizing This book intends to help

the students in getting into the core concepts of Organic Chemistry andencourage them to always ask why something is the case This book woulddirect them to inquire, and find out the answer By taking this approach thestudent will enrich the learning experience, and the information will be

“locked” in their mind so that they are able to face the challenging problems

L Ghatak (Presidency College, Kolkata), who were his teachers, Dr R.C.Sharma, Mr Lokesh Khandelwal, Dr Bikramjit Basu (IIT-Kanpur), Mr.R.K.Bandopadhyaya, Dr.V P Mittal, Mr Pramod Rana, Mr.Ramashish Paul foralways encouraging Amitava to author this book, and for guiding his vision

of serving the ambitions of the students of India

Finally .

In spite of our best efforts this first edition may contain several inadvertenterrors and misprints I hope that you would sincerely pardon the author forthe same andAmitava looks forward to your sincere contributions to keep onimproving this effort

After all a knowledgeable Indian student is a pride for all ofus

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-Amitava Mazumder

May 2006

My mom Mrs Kalyani Mazumder, dad Late Mr Suprasanna KumarMazumder, wife Swati and kids Anuska and Aayush; Mr Mahesh Patil(IPS), Mrs Archana Patil, Mr Pratap Singh (Commisioner, IRS), my siblingSudip, Swagata, Dr Sudeshna, Prof Bikramjit Basu (Prof IISc, Bangalore),Isha Sethi, Mr Sanjeev Sethi (cfo, Star TV), Prof Asish Arora (Physics), Mr.R.K Verma ( MD, Resonance), Mr Jitendra Panda (MD, Peerless, Kolkata).Mrs Sumi, Pratik, and Projwal; thanks to Ms Gabriela Caster and Ms.Preethi.K of Notion Press and their team as a whole

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10) Ether (cyclic, acyclic), thioether

11) Aromatic electrophilic substitution

17) Carboxylic acid derivatives

18) Aliphatic and aromatic nitro compounds19) Amines

IUPAC Nomenclature

In the early days an organic compound was named as per their origin ortheir characteristic property These names are called as common name ortrivial name Take an example like formic acid (HCOOH) It originates fromant & the latin name of ant is formicium and also it behaves like an acid.Thus the name formic acid is given But with increasing number of organiccompounds & complexities name, scientific tools were developed by aninternational body, famously called as International Union of Pure andApplied Chemists in the year 1947 Since then this IUPAC system has beenfollowed to name the compound We will observe while naming the organiccompounds that in some cases trivial names or common name’s have beenretained by IUPAC

Paraffins or alkanes (general formula C n H 2n + 2 ) : First look that there

can be several types of C and H in the simplest alkane There are thecompounds made up single bond between C–atoms (due to its catenationproperty)

1° C means that C, which is attached to only one C Like wise 2°, 3°, 4°and 1°, 2°, 3° H means that corresponding H-atoms are attached to 1° C, 2°

C, 3° C respectively There cannot be any 4° H

Let us introduce the functional groups & their names available in organicchemistry in table-1

Table-1 Names and formulae of functions and classification of acyclic

compounds with examples(G=general, I=IUPAC name)

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Table-2 Some simple alkanes or paraffins

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Olefins or alkenes (General formula C n H 2n ) :

Table-3 Some simple alkenes or olefins

Alkynes (General Formula C n H 2n-2 ) :

Some alkynes or acetylenes

Some simple alicyclic hydrocarbons

Some common benzenoid aromatic hydrocarbons (Arenes)

IUPAC System of nomenclature

1 Unsaturated hydrocarbons

Case-1

Unbranched alkane : Count the number of C–atoms and write the

name depending on number of C–atoms as mentioned in table-2) i.e.for 1–Carbon methane, for 2-carbons ethane etc

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Case-2

Branched alkane : Count the C–atoms in the longest chain and

consider the other radicals as the substituents

The longest chain contains 7-C atoms in the above

Base name is heptane

Now 3 methyl group are in branches so, they are called as substituents

To name them follow the rule that (a) lowest locant rule, in which thealkyl substituent should get minimum locant which ever comes first So,the name of the compound is 3, 4, 5-trimethylpentane

Use hyphen and no gap between number & substituent If there are twodifferent alkyl groups then the seniority will be according to thealphabetical order and listing of name also will be according to thealphabetical order

So, the name is 3-ethyl 4-methylhexane

There is another rule called as lowest sum rule popularly used for theorganic compounds having functional groups, also can be applied here

So, lowest sum in the way shown at the top can give us the rightnumbering The rule tells us that the sum of the locants should be minimum

to write the correct name

Case-3 :

Complex branching with compound substituent : In this case d of

di, t of tri, c of cyclo, i of iso, n of neo has to be considered as the part

of alphabets but not the s of sec, t of tert (i.e tertiary) etc are

considered while determining the alphabetical serniority If acompound possess two or more identical compound substituents then

we use bis, tris, tetrakis, pentakis instead of di, tri, tetra, penta etc.respectively Look at the following examples;

The name is 1, 3, 5 tris (isopropyl) cyclohexane tris (name of theradical) pattern has been followed with the specification of position Wecan also write 1, 3, 5 tris (1-methyl ethyl)cycloclohexane For cyclicmolecules (also acyclic molecules) most substituted part is taken as thebase chain If number of C–atoms is less outisde then the base nameused for cyclic compound.Forexamples ;

Like groups should get similar treatments, so base name is propane andthe name is 1, 3 dicyclo-butylpropane for the last figure

Alkenes, Cyclo alkenes : Priority of double bond is given in a chain With

the branching of alkyl groups, the priority goes to double bond It has noprefix and only shown as suffix (ene) used after the root name

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For the other functional groups the name of the functional groups(common, IUPAC), prefix, suffix in the priority order has been shown in thefollowing table The priority order is followed upto group I

After (amino) group the groups with only prefix are given preferenceaccording to their seniority and according to the alphabetical order and listing

of the same is also according to the alphabetical order

-CO 2 H (carboxylic acid) :

1- Count the C of – CO2 H and put it in the longest chain (look this is aterminal group)

2- Find the base name i.e rest name and add ‘oic acid’ at last and followseniority Take for example;

With cyclic compounds C of CO2 H is not counted in the main chain,therefore use carboxylic acid

For example;

It is a non terminal group Count the C– in the main chain at minimum locant

in simple ketones Otherwise follow the seniority table

For example ;

The above names are retained So derivatives of these compounds will get thebase names of the above compounds

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N-Ethyl–N –methylpropanamine Here we count number of carbon atomsalong the chain having maximum C as the root name (i e alkanamine partcomes from the alkane with longest chain)

Aromatic amines have common names and are used as their base nameswhile writing the names of their derivtives.

IUPAC has retained the common names for aromatic amine like aniline etc.The other groups Cl, Br, I, NO2 etc are used as prefix and seniority depends

on alphabetical seniority of their names Examples ;

Likewise , considering the smaller alkyl group in the alkoxy part and largeralkyl group as alkane, the name of the following compound is ;

If we understand the naming then we can derive structural formula of the

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organic compounds.

Some common as well as IUPAC names of benzene derivatives

General Organic ChemistryIntroduction :

Before going into the chemistry of organic compounds, we will brieflyunderstand the concept of orbitals in a very brief manner and thengradually go into the depth For this we need to have knowledge inphysical chemistry where atomic structure is taught

Concept of orbital :

The mathematical form of the movement of electrons round the nucleusconsidering wave particle duality of electron was given by Schrodinger,which was

Where, y = wave function, (x, y, z) are the variable coordinate positions

of the electron, m= mass of the electron, h= Planck’s constant, E, V aretotal energy and potential energy of the electron respectively

Solving for radial wave functions, we obtain,

where Z = no of protons, a0 = first Bohr’s radius, r = radial distance ofthe electron from the nucleus Therefore radial probability will be R2and characteristic graphs are ,

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Similarly angular wave functions are,

where = angle by the radius with the z- axis in polar coordinate Thereforecombination of R2 gives overall probability of finding an electronaround the nucleus As many properties of atom match with the mathematicaldomain of the orbitals (i.e maximum probability of finding an electron),therefore we can draw the following pictures of the orbitals

From the above diagrams, we should have the following understandings;(1) The orbitals are where we can have maximum probability to find anelectron.

(2) Energywise, 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d etc.according to Aufbau principle

(3) These orbitals house the electrons

(4) When a bond forms of the nature - bond, then pure orbitals with oneelectron unpaired in each comes and make the bond by overlapping oforbitals and probability of electron density in between these two nuclei ismaximum

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(5) - bond can be formed by the participation of hybridised orbitals instead

of pure orbitals

For example C–H bond in CH4 forms by sp3 orbital of C and pure 1sorbital of H The advantage is to explain the bond length, bond angle etc.within the molecules

(6) - bonds form by lateral overlap of orbitals, which are parallel and alsolying in the same plane

(7) Atoms generally undergo hybridisation and then overlap to make - bond

or coordinate covalent bond They accomodate the unpaired electrons inpure orbital/s and - bond forms by lateral overlap of pure orbitals

(8) To remove certain complexities e.g colour of the molecule/s, LCAOMOtheory came into picture It consider number of atomic orbitals taken part inlinear combination = total number of molecular orbitals

Diagramatically the formation of bonding and anti bonding molecular orbitalscan be shown as follows;

Therefore, to explain the formation of Li2 – N2 we consider the followingdiagrams.

For BMO, ABMO diagrams the overlapping can be shown as follows ;

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Structure of molecules of importance and the

hybridisation of atoms.

Electronegativity : This is defined as the tendency of an atom in a molecule

to attract towards itself, the electrons in a chemical bond (actually - bond)e.g inwhere B is more electronegative than A Pauling suggested

electronegativities of A and B EA-E, EA-A EB-B are the bond dissociationenergies in kcal/ mole (1 eV= 23.06 kcal/mole = 96.5 kJ/mole)

Mulliken suggested Here energy values are in eV

effective nuclear charge)

Dipole moment of a bond (i.e bond moment)

If we observe that then A –B bond will have a dipole moment

distance between two nuclei Unit is Debye 1 Debye= 10-18esu cm

% ionic character in - B bond

Also, by Pauling,

% ionic character

Some dipole moment values and directions;

by vectorial addition and considering the

Some more examples are;

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The above result is due to the fact that resonance (discussed later) causesbenzene ring more positive and O atoms of – NO2 more negative

Large charge separation causes more But when there issteric repulsion between O atoms and ortho methyl groups then C– N rotationcauses non planarity of – NO2 group with benzene ring and resonance stops,

ie electron cannot go out side from benzene ring to – NO2 For example,

Here we must understand that the net resultant moment due to the groupmoments lie in the same plane with that of benzene ring and collinear withC1–C4 axis Let us see the other cases below ;

NH2 not along C1 –C4 axis It is at an angle of 70° with the plane of thebenzene ring Therefore, If unsymmetrical groups are present at para, cannever be zero

In organic chemistry, we must understand some effects which govern the

mechanisms and reactions in organic chemistry.

(1) Inductive effect (+I, – I) :

As we know that two different elements if connected by a bond there isalways a pull of the -bp electrons towards one of those two atoms andthereby polarisation occurs at that bond Due to this permanent dipoleinduced in a bond by another bond directly along a chain within a molecule is

towards itself, so it is called – I (electron pair withdrawing) group and otheri.e is supplying the C–Cl electron pair towards Cl, therefore it is

called +I (electron pair repelling) group Magnitude wise, It isfound that inductive effect operates upto C2 strongly from the source and diesdown at C4 +I groups which always supply electron pair can make happythose which are in need of electrons (to be octet for example)

Decreasing order of +I effect,

Here the measurement of I effect is done on the basis of Ingold’s view Anygroup R3C of RCG if decreases electron density in R3C part compared to

R3CH then G is called as + I group, else it is called as – I group

Application of inductive effect will be seen in different sections

2- Field effect :

This effect operates through space or solvent molecules Inductive effect andfield effect are almost the same Field effect still can be identified as itdepends on the geometry of the molecule but inductive effect depends on thenature of bonds

Resonance and Mesomeric effect :

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To explain the stability of many compounds the concept of resonance and ormesomeric effect brought into the picture by scientists Inglold called thisphenomenon as mesomeric effect and Heisenberg termed this as resonanceeffect from the perspective of quantum mechanics Basically both these were

to explain why CO2, benzene (C6H6) etc are stabler than expected

But truely speaking there are differences between these two phenomenawhich we will see later on Thermodynamically, the extra energy by which amolecule is stable, is called as resonance energy and which is,

= observed heat of formation(standard) and = theoretical heat of formation (standard) With thehelp of energy diagram,

For example if we burn benzene, we obtain,

So, there are certain things must be operative To explain that we can drawtwo meaningful resonating structures (also called as cannonical forms) asshown below;

The above change over of the -bonds not only explain the extra stability butalso explain equal bond length between all carboN–Carbon atoms Actually,the more such kinds of structures we can draw more stability appears for thecompound

Examples are ;

Same structures also can be drawn for many aromatic compounds of the type:

Now we are in a position to understand that a molecule is stable if it has

etc type of arrangements In that case we can easily draw manyresonating structures which make it stable Frankly speaking none is theactual representations of actual molecule and only we are presenting themolecule on paper Therefore nothing is resonating as such and actualmolecule’s structure is hybrid of all the the resonating structures

So, to draw resonating structures we must follow the rules mentioned below;

(1) All the cannonical or resonating sturdcure must be Lewis structures, we

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can not write the structures in which C, N has five bonds etc Betweentwo structures we shall use sign.

(2) The positions of the nuclei must be the same in all structures and we are

only allowed to move electrons (unshared or bond pairs)

For example ;

(4) All atoms taking part in resonance, must lie in the same plane or nearly in

the same plane The reason for for this is to gain maximum lateral overlap

(6) Contributing resonating structures: (a) All resonanting structures do

not contribute equally to the true (hybrid) molecule Contribution by one

structure is a function of its own stability

As in the above cases opposite charge separation only by -bond cleavagerequires high energy compared to I or II which are uncharged

(b) Equivalent cannonical forms such as 1(a), 1(b), 1(c) contirbute equally to